Due to the close spacing between adjacent antenna elements no matter at the BS or within each cluster, the resultant mutual antenna coupling brings about the spatial correlation between elements in realistic propagation environments[1]}. Particularly in downlink IoT communications, high correlation between the transmit antennas may occur in the absence of local scattering [2]}. Furthermore, in IoT network, devices or sensors located indoors (e.g., airports, malls, house and buildings) usually suffer from shadowing effects. The shadowing induced by the same obstacle (tree/building) will incur high correlation between propagation paths[3]}. Overlooking the existence of spatial correlation will overestimate the system performance and offer misleading design guide. In order to capture the negative impact of the antenna correlation at transceivers, Kronecker channel model is widely adopted by decomposing the spatial correlation into two independent components, i.e., transmit and receive correlations[4]}. According to the Kronecker model, the channel matrix between the BS and cluster \(k\) , \({{\bf {H}}_{k}}\) , is represented by [5]}, [6]}
\({{\bf {H}}_{k}} = {{\bf R}_r}^{1/2} {\bf H}_w {{\bf R}_t}^{1/2},\) 
